Facebook has some really impressive technology behind them, but they keep expanding in a way that doesn't generate positive revenue. As Facebook becomes more popular, it's likely to need more staff, but at some point it's also just losing more money.
Well, they are looking at $500 million in revenue this year. Sure, their costs are the same order of magnitude, but it's a far cry from not generating revenue.
They have, already, for example, turned into the kind of company where the recruiters are asked to bring in technical candidates with fresh ideas but where the technical interviewers make it clear that conformity is key.
Looking at their hiring practices, it appears they are trying to get serious hackers there. Unfortunately I haven't heard great things about the engineering team from other folks, but none directly from an engineer, so treat that as Valleywag level gossip.